1. Field of the Invention
This invention relates generally to cardiac stimulating apparatus, and more particularly to a method and device for optimizing the cardiac pacing parameters of such apparatus. This invention finds particular use with cardiac stimulators for use by patients suffering from chronic congestive heart failure (CHF) and having an unacceptably low cardiac output.
2. Discussion of the Prior Art
Patients suffering from CHF typically manifest a degraded cardiac function, such as an abnormally low cardiac output. While adaptive rate pacing may be utilized to increase cardiac output by increasing heart rate with increased metabolic demand, such an increased heart rate necessitates that the heart work harder to pump a sufficient quantity of blood to meet the needs of the body. Patients suffering from CHF may not have sufficient reserve to accommodate the higher rate.
Prior art manual and automated techniques are known whereby one or more of the pacing cycle parameters of a cardiac stimulator, such as R--R interval, A-V delay, and pacing mode can be adjusted to help optimize cardiac output and cardiac pressure parameters for a given pacing rate.
One standard current approach is to use a pacing system analyzer under manual control while monitoring one or more physiological variables. The pacing system parameters are manually varied and the optimum value is assumed to be that at which the maximum (or occasionally, minimum) value of the physiological variable occurred. There are several disadvantages to this approach. First, this manual method is overly time-consuming. Secondly, data gathering is not automated, thus resulting in possible errors during the data transcription. Thirdly, during the time of the procedure, the underlying physiologic substrate may change resulting in inaccurate assessment of cardiac performance. The effect is exacerbated by the length of the procedure.
One such automated technique is disclosed in U.S. Pat. No. 5,024,222 to Thacker. The pertinent aspect of this patent involves scanning through a series of available A-V pulse delays at a fixed heart rate, while monitoring a measure of cardiac output, and then setting the A-V pulse delay to the value which resulted in the maximum cardiac output. The drawback with this automated technique for pacing parameter optimization is that the body's natural reflexes have time to respond to each pacing parameter setting, potentially masking differences between settings. In addition, this technique does not include monitoring of the underlying substrate by returning often to a baseline or intrinsic heart conditions.
U.S. Pat. No. 4,303,075 to Heilman, et al. discloses a method and apparatus for maximizing stroke volume through atrio-ventricular pacing using implanted cardioverter/pacer. This patent discloses optimizing the A-V pulse delay by maximizing the measured value of a parameter, e.g., stroke volume measured by electrical impedance. For additional background on the impact of implementing different A-V pulse delays on cardiac function in a patient with congestive heart failure (CHF), reference is made to an article authored by H. Kataoka, entitled "Hemodynamic Effect of Physiological Dual-Chamber Pacing in a Patient with End Stage Dilated Cardiomyopathy": "A Case Report", PACE, 14:1330-1335 (09/1991).
The optimization of pacing parameters is not as critical in patients with relatively normal, healthy hearts. These patients have the necessary cardiac reserve to compensate for programming errors. It is patients with depressed cardiac function that are much more sensitive to factors such as pacing rate and A-V delay. Current optimization techniques, if they are used at all, are time-consuming and prone to error.
The present invention permits the rapid and accurate automated determination of optimum pacemaker (or AICD) settings. These settings can be either automatically determined and established by the pacemaker device, or determined by an external programmer/monitor and later programmed into the pacemaker device, which is already implanted or subsequently implanted by a physician.